Quantum cascade lasers emitting in the 3.8-µm range

Quantum cascade lasers (QCLs) emitting at a wavelength of 3.8  μm were designed, fabricated, and characterized to provide efficient and compact sources for various mid-infrared applications, including free-space optical communication, gas sensing, and infrared countermeasures. The devices are based on strain-balanced InGaAs/AlInAs heterostructures grown on InP substrates. High-resolution X-ray diffraction confirmed excellent crystalline quality and precise layer periodicity. Ridge waveguide devices with high-reflectivity (HR) facet coatings demonstrated low threshold current densities, high slope efficiencies, and stable emission near 3.8  μm under both pulsed and continuous-wave (CW) operation at room temperature. Devices with a ridge width of 5  μm and a cavity length of 4  mm, featuring HR coatings, delivered CW powers exceeding 0.45  W at 300  K, with a threshold current density of 2.2 kA/cm². The combination of HR coatings and optimized epilayer-down mounting significantly improved thermal management, enabling robust performance and enhanced output power stability. These results confirm the viability of short-wavelength QCLs for mid-infrared photonic systems, particularly in applications requiring compactness, spectral selectivity, and thermal resilience.